hw/ac97: Make a bunch of mixer registers read only
The Linux ac97 driver tries to see if optional things like video input volume control are available in 2 ways: 1) See if the mute bit is set after reset, if it is no further tests are done 2) If the mute bit is not set it does a write/read test of the mute bit This patch changes our ac97 to conform to what the Linux driver expects, it initializes registers for things which we don't emulate to 0 (so the mute bit is not set) and makes them read only. This causes Linux to now longer show the following (functionless) controls in alsamixer: Master Mono vol + mute 3d Control toggle PCM out pre / post 3d select Surround toggle CD vol + mute Mic vol + mute Mic boost toggle Mic mic1 / mic2 select Video vol + mute Phone vol + mute Beep mono vol + mute Aux vol + mute Mono "output mic" / "mix" select Sigmatel 4 speaker stereo toggle Sigmatel ADC 6Db att toggle Sigmatel DAC 6Db att toggle This patch was also tested with a Windows XP guest and there it also makes a number of functionless mixer controls go away. Signed-off-by: NHans de Goede <hdegoede@redhat.com> Signed-off-by: Nmalc <av1474@comtv.ru>
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